It is known that DRAM devices and ferroelectric memory devices use capacitors for data storage. Typical capacitors include two electrodes and a dielectric film between the two electrodes. With the recent trend toward higher integration density of semiconductor devices, capacitors having a cylindrical lower electrode have been developed (to provide increased capacitance).
In recent years, methods of forming a lower capacitor electrode made of titanium nitride have been suggested. Since titanium nitride has a low reactivity with dielectric substance and a low resistivity, a lower capacitor electrode adopting a high-k dielectric film or ferroelectric film of a high reactivity may be made of titanium nitride.
A conventional method of forming a lower electrode of a capacitor will now be described with reference to FIG. 1. As illustrated in FIG. 1, a mold layer 2 is formed on a semiconductor substrate 1. The mold layer 2 is patterned to form a recess 3. The mold layer 2 can be silicon oxide. A titanium nitride layer 4 is conformally formed on an entire surface of the semiconductor substrate 1. A sacrificial insulation layer 5 is formed on the titanium nitride layer 4. The sacrificial insulation layer 5 can be silicon oxide.
As illustrated in FIG. 2, the sacrificial insulation layer 5 is planarized until the titanium nitride layer 4 on the mold layer 2 is exposed to form a sacrificial insulation pattern 5a in the recess 3. The exposed titanium nitride layer 4 is etched until a top surface of the mold layer 2 is exposed to form a cylindrical lower electrode 4a in the recess 3.
It is known to use Chlorine-series gases to etch titanium nitride layers. Korean Patent Application No. 2003-22361 discusses that if titanium nitride is etched using a chlorine-series gas, a high etch rate can be obtained. If chlorine of a chlorine gas is coupled with titanium of the titanium nitride layer 4, titanium chloride (TiCl4) is produced. Thus, a high etch rate for the titanium nitride layer 4 is obtained due to the etch gas containing the chlorine gas.
It is known that silicon oxide has a low etch rate using the chlorine gas. For this reason, if a portion of the sacrificial insulation layer 5 remains on the exposed titanium nitride layer 4, the exposed titanium nitride layer 4 (covered by the remaining sacrificial insulation layer 5) may not be etched.
It is known that, the etch gas may further contain argon gas to reduce the above problem. That is, an ion collision energy is enhanced to etch gases containing the chlorine and argon gases to remove the sacrificial insulation layer 5 remaining on the exposed titanium nitride layer 4 and to etch the expose titanium nitride layer 4.
If the titanium nitride layer 4 is etched using the above referenced etching, a “sharp” portion 6 of the lower electrode 4a may be formed. That is, the anisotropic etching characteristic of the plasmarized chlorine and argon gases is strengthened due to the enhanced ion collision energy. Accordingly, an upper portion of a sidewall of the lower electrode 4a is etched like a spacer to form the sharp portion 6, which may result in the electric field concentrates thereat which may increase leakage current.